Control mechanism for variable throw hydraulic pumps



June 20, 1939. w BQDDY 2,163,479

CONTROL MECHANISM FOR VARIABLE THROW HYDRAULIC PUMPS Filed May 28, 1958 2 Sheets-Sheet 1 Mum June 2 0, 1939. w BODDY 2,163,479

CONTROL MECHANISM FOR VARIABLE THROW HYDRAULIC PUMPS Filed May 28, 1938 2 Sheets-Sheet 2 f VII //7 mar? Patented June 20, 1939 UNITED STATES PATENT OFFICE CONTROL MECHANISM FOR VARIABLE THROW HYDRAULIC PUMPS Application May 28, 1938, Serial No. 210,727 In Great Britain June 1, 1937 3 Claims.

This invention relates to control mechanism for variable throw hydraulic pumps of the kind in which a part is moved either directly or by actuating a hydraulic or other relay mechanism,

5 to control the maximum pump delivery pressure.

With control mechanism, as hitherto employed, the pump when stopped is left at maximum stroke setting by the control mechanism and on starting up again, the pump driving motor has to cause the pump to overcome the normal maximum delivery pressure before pump throw adjustment is effected. This is liable to damage the driving motor through overloading. In order to prevent this, electrically or otherwise operated by-pass valves have been employed to reduce the pump delivery pressure when starting up.

The object of the present invention is to obviate the danger of overloading the pump driving motor when starting up, whilst avoiding the complication of providing automatic by-pass valves.

The invention comprises the provision of means which when the pump stops reduces to a predetermined minimum the loading pressure against which the variable throw control member works and when the pump starts builds up such pressure at an adjustable rate, so that the pump throw which is the maximum at starting is gradually reduced as the pump delivery pressure increases to the normal maximum at which it is to be maintained.

Referring to the accompanying explanatory drawings:

Figure 1 is a longitudinal sectional elevation of pump control mechanism constructed and arranged in one convenient form in accordance with this invention.

Figure 2 is a general view of a pump with control unit in accordance with this invention.

In the arrangement illustrated, the piston valve a (which is shown in its mid or balance position) is adapted to control the supply of pressure fluid from a pipe I) to one or other of two outlet branches 0, c which deliver it to one or other of two cylinders containing single acting pistons or to the opposite ends of a cylinder containing a double action piston. Such pistons or piston control the throw of a variable throw hydraulic pump in any known manner. The piston valve :1 also controls the exhaustion of pressure fluid from the cylinders or cylinder ends in the usual manner.

The movement of the piston a is effected by the lever d fulcrumed at e and connected to a rod f secured to a part 9 which I will term a plunger. Within the latter is a stationary piston h, to the passage h within which pressure fluid is supplied by the pipe n from the delivery main i of the variable throw hydraulic pump located in the casing 7, Figure 4. The pipe or branch I) also receives its pressure fluid from the main i.

Between the flanged end is of the plunger g and the end of the skirt of piston m is a compression spring n.

The cylinder 0 in which the piston m moves, receives pressure fluid from the pump delivery main 2' by way of the pipe b and the branch connection p, the rate of flow of pressure fluid into the cylinder 0 being regulated by the needle valve q. When the pressure in the delivery main ifalls, due to stoppage of the pump, there is 15 a rapid release of pressure from the cylinder 0 back to the branch 13, pipe b, and main 1', by way of the non-return valve r. The piston m has a shoulder s which acts as a stop and as a valve with respect to a ridge t around the cylinder 0, 20 so that when the piston is moved to its final position by the fluid pressure in the cylinder, leakage of fluid along the piston is prevented.

The operation of the control apparatus will be understood from the following: 25

When the variable throw pump is stopped, the pressure in the cylinder 0 is released by way of the non-return valve 1' and the piston m is forced by the spring n to its right hand position, thus permitting the control spring n to increase in 30 length when it exerts a considerably reduced pressure against the plunger g. As there is an absence of pressure in the passage h the plunger g is at its left hand position and this by means of the lever d causes the valve or to be in its right 35 hand position, with the port 0 open to the pressure fluid inlet branch. This is the position in which if pressure fluid were available, such fluid passing through the passage 0 to the servo motor which adjusts the variable throw mechanism, 40 would cause said motor to increase the'pump throw. When the drive to the variable throw pump is restarted, the pump builds up its delivery pressure to a reduced value due to the resetting of the variable throw control mechanism conse- 45 quent upon the actions above described. When the reduced pressure corresponding to the reduced compression of the spring n is reached, such pressure acting on the plunger g moves the latter to the right and by means of the lever d moves the 50 valve (1 to the left, which opens the branch 0 to pressure fluid and the branch c to exhaust, thereby causing the servo motor (which adjusts the variable throw mechanism of the pump) to reduce the pump throw as the pump speeds up, so 55 that the pressure is maintained at the reduced value. During this time, the delivery pressure is being built up in the cylinder 0 by way of the needle valve q and the piston m is being moved to the left which increases the compression of the spring 12 and increases the hydraulic pressure required in the passage h to balance the spring pressure and to cause movement of the plunger 7. The control mechanism is therefore allowing the pump to build up a higher delivery pressure, the maximum pressure being reached when the piston m is in its extreme left hand position with the shoulder s seated on the ridge t.

It will be seen that until the piston m is in its extreme left hand position, (the length of time taken for it to reach there being adjustable by the setting of the needle valve q) the valve a is moved to cause reductions in the pump throw by delivery pressures below the maximum pressure which the pump is designed to maintain normally. Thus the final pressure is gradually built up, which condition obviates the overloading of the pump driving motor at starting.

The control of the variable throw mechanism may be effected by means other than the hydraulic control valve and motor before described.

With my improvement, whereas the control is eifected normally during the operation of the variable throw pump, I ensure that if the pump delivery ceases, the variable throw mechanism is automatically reset so that the pump works under reduced pressure throw conditions and so overloading and other diiiiculties at starting are overcome.

What I claim is:

1. Mechanism for operating a variable throw control member for a variable throw hydraulic pump, comprising a piston, a hydraulic connection from the delivery side of said pump to one side of said piston, a compression spring acting upon the other side of said piston, a further piston of larger area than said first mentioned piston constituting an abutment for the other end of said compression spring, means to limit the travel of said further piston towards the first mentioned piston, a hydraulic connection from the delivery side of said pump to the side of said further piston remote from said compression spring, an adjustable constriction in said last mentioned connection, a by-pass duct around said constriction and a non-return valve to permit flow of fiuid from said further piston to the said delivery side of said pump in said by-pass duct.

2. Mechanism for operating a variable throw control member for a variable throw hydraulic pump comprising a plunger, a piston co-axial therewith and of larger effective area than said plunger, a cylinder wherein said piston works, a compression spring acting between said plunger and piston, conduits to lead pressure fluid from the delivery side of said pump to the sides of both said plunger and pump remote from said spring, a ridge upon the wall of said cylinder constituting a seating engaged by said piston after predetermined movement towards said plunger, a rod upon said plunger do-axial therewith and extending towards and into said piston, a slot in the skirt in said piston, a slot in said cylinder in line with said slot, a lever pivoted to said rod and to said variable throw control member and passing through said slots, a needle valve in the said conduit leading to the said piston, a conduit bypassing said non-return valve and a non-return valve located in said by-pass conduit and opening to exhaust fluid from said piston.

3. Mechanism for operating a variable throw control member for a variable throw hydraulic pump, comprising resilient means arranged to constrain said member towards maxim-um throw position, means responsive to the delivery pressure of said pump acting against the force of said resilient means to move said control member away from maximum throw position on increase of said delivery pressure beyond a predetermined maximum, means likewise responsive to said pump delivery pressure to increase the force of said resilient means and means to restrict to a controllable degree the rate of response of the last mentioned pressure responsive means to increase only of pump delivery pressure.

WILLIAM HENRY BODDY. 

